For the past month, monarch butterflies have caused a lot of buzz in both the news and in conservation circles. The reason: a report published by the World Wildlife Fund and others that documented a 59 percent decline in monarch populations this year.

It’s well known that almost the entire eastern population of monarch butterflies overwinters in a few clustered forests in Mexico. These tiny islands of habitat make the butterflies vulnerable. Many U.S. residents believe that the population decline is, in fact, due to logging in Mexican forests. But as Taylor points out, the Mexican government has done an excellent job stopping illegal logging.

So why the decline?

The study’s authors point to agricultural fields. Taylor suggests that the monarch butterfly is likely “collateral damage” from the use of genetically engineered crops, namely Roundup-ready corn and soybeans. These crops have resulted in significantly higher pesticide use, wiping out the milkweeds that monarchs need to survive.

As Taylor says in the interview:

Now you are really hard pressed to find any corn or soybeans that have milkweed in the fields. I haven’t seen any for years now because of the use of Roundup after they planted these crops. They have effectively eliminated milkweed from almost all of the habitat that monarchs used to use.

Additionally, due to biofuel and high crop prices, there are more acres in corn and soybean production than any year since just after World War II. This has meant that a lot of land has been taken out of the Conservation Reserve Program (CRP) and a lot of marginal land–where milkweeds once grew– has been tilled.

That’s a lot of lost habitat for wildlife, including monarch butterflies.

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